Most semiconductor fabrication processes (e.g., plasma etch, physical-vapor deposition, ion implant, micro lithography, plasma-enhanced chemical-vapor deposition, photoresist ash, etc.) in integrated circuit manufacturing have moved to single-wafer fabrication equipment in order to meet the stringent process control requirements for state-of sub-half micron semiconductor technologies. However, batch (or multi-wafer) furnaces still dominate thermal processing applications due to their throughput and relatively mature manufacturing equipment technology. Rapid Thermal Processing (RTP) provides single-wafer fabrication alternative to batch furnaces for various thermal processes used in semiconductor manufacturing processes, including rapid thermal anneals (e.g., transistor source/drain junction formation, implant anneal processes, and silicide formation), rapid thermal oxidation, and rapid thermal chemical-vapor deposition (RTCVD) processes (e.g., for deposition of polysilicon, silicon dioxide, silicon nitride, and amorphous silicon).
RTP systems usually employ optical or infrared pyrometry in order to measure the wafer temperature. Conventional RTP systems using pyrometry sensors suffer from wafer temperature uniformity and repeatability problems caused by emissivity-related pyrometry temperature measurement errors and lack of dynamic real-time wafer temperature uniformity control. The current inventors have also invented devices and methods for real-time measurement and compensation of pyrometry effects (in U.S. Pat. Nos. 5,443,315 and 5,444,815 that are hereby incorporated by reference). Even with real-time capability for compensation of the wafer emissivity effects, pyrometry sensors may experience long-term drift in their response, requiring corrective actions. Thus, RTP systems require frequent pyrometry sensor calibrations in order to ensure accurate and repeatable temperature measurements and to enable reliable temperature control. Precision calibrated pyrometry sensors are essential for dynamic wafer temperature uniformity control when using multi-point pyrometry probes in multi-zone RTP systems.
Conventional pyrometry calibration techniques typically employ wafers with bonded or electron-beam welded thermocouples (to be called TC-bonded wafers). TC-bonded wafers with one or multiple bonded thermocouples (usually Type K thermocouples with 0.005" diameter wires) are used to calibrate multiple point pyrometry probes. TC-bonded wafers with multiple bonded thermocouples require manual handling and manual loading inside the RTP process chamber. The thermocouple wires are manually extended from the bonded junctions on the wafer inside the RTP process chamber to the interface electronics and data acquisition system located outside the RTP chamber. This elaborate and time-consuming manual procedure employed in conventional RTP temperature sensor calibration methods has numerous drawbacks and limitations, particularly in semiconductor production environments.
One major drawback is the negative impact on overall equipment effectiveness and utilization. Manual loading and unloading of a TC-bonded wafer can result in significant equipment downtime and interruption of production flow. This resulting reduction in tool utilization and availability for production uses can increase the RTP equipment cost of ownership (CoO). Moreover, TC-bonded wafers are expensive (as much as several thousand dollars for wafers with several bonded thermocouples) and have limited thermal cycling lifetimes (particularly at higher temperatures such as T&gt;.about.900.degree. C. and/or in reactive oxidizing environments). This problem can further increase the RTP Cost-of-Ownership (CoO expressed as cost in dollars per wafer processed) due to increased cost of consumables for the RTP equipment.
Another problem with conventional RTP pyrometry sensor calibration techniques is the need to break the chamber vacuum in vacuum RTP systems (such as the RTP modules used in silicide and metallization cluster tools) when manually loading and unloading the TC-bonded wafers. In vacuum RTP systems, breaking the chamber vacuum requires a subsequent post-calibration chamber pump-down cycle in order to reestablish the chamber base pressure and required vacuum integrity. The extended equipment downtime due to the vent and pump cycles can increase the CoO.
Another significant problem with conventional RTP pyrometry sensor calibration techniques is exposing the RTP process chamber to the external atmospheric environment. Exposure of the process chamber to the external ambient environment can lead to moisture adsorption and contaminant introduction into the RTP process chamber. Contaminants that enter the process chamber can lead to contaminated wafers during production and subsequent manufacturing yield loss. Additionally, manual handling and loading/unloading of the TC-bonded wafer further increases the chance of progressively contaminating the TC-bonded wafer and subsequently compromising the RTP process chamber cleanliness. This can result in manufacturing yield loss and further degradation of the RTP CoO due to increased wafer defect density.